The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Jürg Alexander Schiffmann - One of the best experts on this subject based on the ideXlab platform.
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Design of Oil-Free Turbocompressors for a Two-Stage Industrial Heat Pump under Variable Operating Conditions
2016Co-Authors: Adeel Javed, Cordin Arpagaus, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:A pair of mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the Turbocompressors. The present paper will guide the readers through different stages of the design process of such Turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.
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Two-Stage Heat Pump using Oil-Free Turbocompressors - System Design and Simulation
2016Co-Authors: Cordin Arpagaus, Adeel Javed, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:The combination of multi-stage heat pump cycles with small-scale oil-free turbocompressor technology running on gas bearings could be a promising way to increase performance in domestic and commercial heat pumps. This paper presents a novel two-stage heat pump system with two heat sources at two different temperature levels using two separate Turbocompressors rotating on gas bearings optimized for R134a. The system allows integration of unused heat sources, e.g. solar thermal or waste heat, into heat production with a minimal loss of exergy. The cycle comprises an evaporator for the first heat source, a condenser as heat sink, an open economizer with integrated heat exchanger for the second heat source, and a tube-in-tube suction line heat exchanger (SHX) in the high-pressure for superheating and subcooling. The aim of this study is to evaluate theoretically the performance of this heat pump cycle using a system model programmed in the software EES (Engineering Equations Solver). The simulation assumes steady-state, negligible pressure drops and heat losses, and adiabatic expansion processes. The superheating in the evaporator and the SHX is 5°C, and there is no subcooling in the condenser. The heat exchangers are modeled using effectiveness-NTU models. At the design point, the heating capacity of the condenser is set to 6.5 kW and provides hot water of 55°C. The first heat source is brine of 5°C. The second heat source is water of 30°C and has been designed to provide up to 30% of the total condenser heat capacity. The two Turbocompressors are designed specifically to meet the heat pump design point. Presently, one-dimensional (1D) compressor maps are used in the heat pump model. Simulation results show that coefficient of performance (COP) improvements of 20% to 30% are achievable, depending on the source temperature levels of the heat pump cycle and the amount of second heat source added to the system. The COP increases with higher source temperatures, higher second heat source capacity, and lower sink temperature. The pressure ratios are defined by the imposed temperature levels. The mass flow rate of the refrigerant in the first stage is mainly determined by the second heat source capacity, and in the second stage by the heat capacity of the condenser. In future work, this novel heat pump concept will be tested experimentally.
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Small-scale Turbocompressors for wide-range operation with large tip-clearances for a two-stage heat pump concept
International Journal of Refrigeration, 2016Co-Authors: Adeel Javed, Stefan Bertsch, Cordin Arpagaus, Jürg Alexander SchiffmannAbstract:Two mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been theoretically designed for a 6.5 kW two-stage heat pump functioning under variable operating conditions. The novelty in the heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused heat from various secondary heat sources. Managing the heat pump operational deviations with the secondary heat is difficult for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge, choke and maximum rotational speed margins. Furthermore, regulating the tip-leakage flow caused by large tip-clearances in small-scale turbomachinery is challenging. This paper will guide the readers through different stages of the design process of small-scale Turbocompressors subjected to different operational and design constraints. The design review and the presented methodology will help the designers make suitable parameter selections for achieving high efficiency and wide compressor operating range.
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Integrated Design and Multi-objective Optimization of a Single Stage Heat-Pump Turbocompressor
Journal of Turbomachinery, 2015Co-Authors: Jürg Alexander SchiffmannAbstract:Small-scale turbomachines in domestic heat pumps reach high efficiency and provide oil-free solutions, which improve heat-exchanger performance and offer major advantages in the design of advanced thermodynamic cycles. An appropriate turbocompressor for domestic air based heat pumps requires the ability to operate on a wide range of inlet pressure, pressure ratios, and mass flows, confronting the designer with the necessity to compromise between range and efficiency. Further, the design of small-scale direct driven turbomachines is a complex and interdisciplinary task. Textbook design procedures propose to split such systems into subcomponents and to design and optimize each element individually. This common procedure, however, tends to neglect the interactions between the different components leading to suboptimal solutions. The author proposes an approach based on the integrated philosophy for designing and optimizing gas bearing supported, direct driven Turbocompressors for applications with challenging requirements with regards to operation range and efficiency. Using experimentally validated reduced order models for the different components an integrated model of the compressor is implemented and the optimum system found via multi-objective optimization. It is shown that compared to standard design procedures, the integrated approach yields an increase of the seasonal compressor efficiency of more than 12 points. Further, a design optimization based sensitivity analysis allows to investigate the influence of design constraints determined prior to optimization such as impeller surface roughness, rotor material, and impeller force. A relaxation of these constrains yields additional room for improvement. Reduced impeller force improves efficiency due to a smaller thrust bearing mainly, whereas a lighter rotor material improves rotordynamic performance. A hydraulically smoother impeller surface improves the overall efficiency considerably by reducing aerodynamic losses. A combination of the relaxation of the three design constraints yields an additional improvement of six points compared to the original optimization process. The integrated design and optimization procedure implemented in the case of a complex design problem thus clearly shows its advantages compared to traditional design methods by allowing a truly exhaustive search for optimum solutions throughout the complete design space. It can be used for both design optimization and for design analysis.
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Integrated Design and Multi-Objective Optimization of a Single Stage Heat-Pump Turbocompressor
Volume 3B: 39th Design Automation Conference, 2013Co-Authors: Jürg Alexander SchiffmannAbstract:Small scale turbomachines in domestic heat pumps reach high efficiency and provide oil-free solutions which improve heat-exchanger performance and offer major advantages in the design of advanced thermodynamic cycles. An appropriate turbocompressor for domestic air based heat pumps requires the ability to operate on a wide range of inlet pressure, pressure ratios and mass flows, confronting the designer with the necessity to compromise between range and efficiency. Further the design of small-scale direct driven turbomachines is a complex and interdisciplinary task. Textbook design procedures propose to split such systems into subcomponents and to design and optimize each element individually. This common procedure, however, tends to neglect the interactions between the different components leading to suboptimal solutions. The authors propose an approach based on the integrated philosophy for designing and optimizing gas bearing supported, direct driven Turbocompressors for applications with challenging requirements with regards to operation range and efficiency. Using previously validated reduced order models for the different components an integrated model of the compressor is implemented and the optimum system found via multi-objective optimization. It is shown that compared to standard design procedure the integrated approach yields an increase of the seasonal compressor efficiency of more than 12 points. Further a design optimization based sensitivity analysis allows to investigate the influence of design constraints determined prior to optimization such as impeller surface roughness, rotor material and impeller force. A relaxation of these constrains yields additional room for improvement. Reduced impeller force improves efficiency due to a smaller thrust bearing mainly, whereas a lighter rotor material improves rotordynamic performance. A hydraulically smoother impeller surface improves the overall efficiency considerably by reducing aerodynamic losses. A combination of the relaxation of the 3 design constraints yields an additional improvement of 6 points compared to the original optimization process. The integrated design and optimization procedure implemented in the case of a complex design problem thus clearly shows its advantages compared to traditional design methods by allowing a truly exhaustive search for optimum solutions throughout the complete design space. It can be used for both design optimization and for design analysis.
Adeel Javed - One of the best experts on this subject based on the ideXlab platform.
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Design of Oil-Free Turbocompressors for a Two-Stage Industrial Heat Pump under Variable Operating Conditions
2016Co-Authors: Adeel Javed, Cordin Arpagaus, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:A pair of mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the Turbocompressors. The present paper will guide the readers through different stages of the design process of such Turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.
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Two-Stage Heat Pump using Oil-Free Turbocompressors - System Design and Simulation
2016Co-Authors: Cordin Arpagaus, Adeel Javed, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:The combination of multi-stage heat pump cycles with small-scale oil-free turbocompressor technology running on gas bearings could be a promising way to increase performance in domestic and commercial heat pumps. This paper presents a novel two-stage heat pump system with two heat sources at two different temperature levels using two separate Turbocompressors rotating on gas bearings optimized for R134a. The system allows integration of unused heat sources, e.g. solar thermal or waste heat, into heat production with a minimal loss of exergy. The cycle comprises an evaporator for the first heat source, a condenser as heat sink, an open economizer with integrated heat exchanger for the second heat source, and a tube-in-tube suction line heat exchanger (SHX) in the high-pressure for superheating and subcooling. The aim of this study is to evaluate theoretically the performance of this heat pump cycle using a system model programmed in the software EES (Engineering Equations Solver). The simulation assumes steady-state, negligible pressure drops and heat losses, and adiabatic expansion processes. The superheating in the evaporator and the SHX is 5°C, and there is no subcooling in the condenser. The heat exchangers are modeled using effectiveness-NTU models. At the design point, the heating capacity of the condenser is set to 6.5 kW and provides hot water of 55°C. The first heat source is brine of 5°C. The second heat source is water of 30°C and has been designed to provide up to 30% of the total condenser heat capacity. The two Turbocompressors are designed specifically to meet the heat pump design point. Presently, one-dimensional (1D) compressor maps are used in the heat pump model. Simulation results show that coefficient of performance (COP) improvements of 20% to 30% are achievable, depending on the source temperature levels of the heat pump cycle and the amount of second heat source added to the system. The COP increases with higher source temperatures, higher second heat source capacity, and lower sink temperature. The pressure ratios are defined by the imposed temperature levels. The mass flow rate of the refrigerant in the first stage is mainly determined by the second heat source capacity, and in the second stage by the heat capacity of the condenser. In future work, this novel heat pump concept will be tested experimentally.
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Small-scale Turbocompressors for wide-range operation with large tip-clearances for a two-stage heat pump concept
International Journal of Refrigeration, 2016Co-Authors: Adeel Javed, Stefan Bertsch, Cordin Arpagaus, Jürg Alexander SchiffmannAbstract:Two mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been theoretically designed for a 6.5 kW two-stage heat pump functioning under variable operating conditions. The novelty in the heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused heat from various secondary heat sources. Managing the heat pump operational deviations with the secondary heat is difficult for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge, choke and maximum rotational speed margins. Furthermore, regulating the tip-leakage flow caused by large tip-clearances in small-scale turbomachinery is challenging. This paper will guide the readers through different stages of the design process of small-scale Turbocompressors subjected to different operational and design constraints. The design review and the presented methodology will help the designers make suitable parameter selections for achieving high efficiency and wide compressor operating range.
Yu. K. Yakimovich - One of the best experts on this subject based on the ideXlab platform.
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A study of the characteristics of a power installation with a compact cylindrical steam generator and a turbocompressor
Thermal Engineering, 2002Co-Authors: K. A. Yakimovich, A. G. Mozgovoi, V. A. Fomin, Yu. K. YakimovichAbstract:The experimentally obtained characteristics of a power installation, which consists of a compact cylindrical steam generator and a turbocompressor, are analyzed. The concept of the efficient drag coefficients for each part of the installation is introduced. The approximating equations for the total characteristics of the installation are found.
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Problems of starting up and control of a power unit based on a small-scale cylindrical steam generator and a turbocompressor
Thermal Engineering, 2001Co-Authors: K. A. Yakimovich, A. G. Mozgovoi, V. A. Fomin, Yu. K. YakimovichAbstract:The possibility for using small-scale cylindrical steam generators (SCSGs) with a turbocompressor is examined from the point of view of the pressure drop in the air-gas path and the problems of starting up and control of the installation. The arrangement of the installation with a built-in or an external auxiliary combustion chamber is considered, and the results of tests of the SCSG unit with a turbocompressor and an external auxiliary combustion chamber are presented.
Cordin Arpagaus - One of the best experts on this subject based on the ideXlab platform.
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Design of Oil-Free Turbocompressors for a Two-Stage Industrial Heat Pump under Variable Operating Conditions
2016Co-Authors: Adeel Javed, Cordin Arpagaus, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:A pair of mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the Turbocompressors. The present paper will guide the readers through different stages of the design process of such Turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.
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Two-Stage Heat Pump using Oil-Free Turbocompressors - System Design and Simulation
2016Co-Authors: Cordin Arpagaus, Adeel Javed, Stefan S. Bertsch, Jürg Alexander SchiffmannAbstract:The combination of multi-stage heat pump cycles with small-scale oil-free turbocompressor technology running on gas bearings could be a promising way to increase performance in domestic and commercial heat pumps. This paper presents a novel two-stage heat pump system with two heat sources at two different temperature levels using two separate Turbocompressors rotating on gas bearings optimized for R134a. The system allows integration of unused heat sources, e.g. solar thermal or waste heat, into heat production with a minimal loss of exergy. The cycle comprises an evaporator for the first heat source, a condenser as heat sink, an open economizer with integrated heat exchanger for the second heat source, and a tube-in-tube suction line heat exchanger (SHX) in the high-pressure for superheating and subcooling. The aim of this study is to evaluate theoretically the performance of this heat pump cycle using a system model programmed in the software EES (Engineering Equations Solver). The simulation assumes steady-state, negligible pressure drops and heat losses, and adiabatic expansion processes. The superheating in the evaporator and the SHX is 5°C, and there is no subcooling in the condenser. The heat exchangers are modeled using effectiveness-NTU models. At the design point, the heating capacity of the condenser is set to 6.5 kW and provides hot water of 55°C. The first heat source is brine of 5°C. The second heat source is water of 30°C and has been designed to provide up to 30% of the total condenser heat capacity. The two Turbocompressors are designed specifically to meet the heat pump design point. Presently, one-dimensional (1D) compressor maps are used in the heat pump model. Simulation results show that coefficient of performance (COP) improvements of 20% to 30% are achievable, depending on the source temperature levels of the heat pump cycle and the amount of second heat source added to the system. The COP increases with higher source temperatures, higher second heat source capacity, and lower sink temperature. The pressure ratios are defined by the imposed temperature levels. The mass flow rate of the refrigerant in the first stage is mainly determined by the second heat source capacity, and in the second stage by the heat capacity of the condenser. In future work, this novel heat pump concept will be tested experimentally.
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Small-scale Turbocompressors for wide-range operation with large tip-clearances for a two-stage heat pump concept
International Journal of Refrigeration, 2016Co-Authors: Adeel Javed, Stefan Bertsch, Cordin Arpagaus, Jürg Alexander SchiffmannAbstract:Two mechanically driven small-scale Turbocompressors running on gas lubricated bearings have been theoretically designed for a 6.5 kW two-stage heat pump functioning under variable operating conditions. The novelty in the heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused heat from various secondary heat sources. Managing the heat pump operational deviations with the secondary heat is difficult for the Turbocompressors. The Turbocompressors can potentially exceed their operating range defined by the surge, choke and maximum rotational speed margins. Furthermore, regulating the tip-leakage flow caused by large tip-clearances in small-scale turbomachinery is challenging. This paper will guide the readers through different stages of the design process of small-scale Turbocompressors subjected to different operational and design constraints. The design review and the presented methodology will help the designers make suitable parameter selections for achieving high efficiency and wide compressor operating range.
K. A. Yakimovich - One of the best experts on this subject based on the ideXlab platform.
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A study of the characteristics of a power installation with a compact cylindrical steam generator and a turbocompressor
Thermal Engineering, 2002Co-Authors: K. A. Yakimovich, A. G. Mozgovoi, V. A. Fomin, Yu. K. YakimovichAbstract:The experimentally obtained characteristics of a power installation, which consists of a compact cylindrical steam generator and a turbocompressor, are analyzed. The concept of the efficient drag coefficients for each part of the installation is introduced. The approximating equations for the total characteristics of the installation are found.
-
Problems of starting up and control of a power unit based on a small-scale cylindrical steam generator and a turbocompressor
Thermal Engineering, 2001Co-Authors: K. A. Yakimovich, A. G. Mozgovoi, V. A. Fomin, Yu. K. YakimovichAbstract:The possibility for using small-scale cylindrical steam generators (SCSGs) with a turbocompressor is examined from the point of view of the pressure drop in the air-gas path and the problems of starting up and control of the installation. The arrangement of the installation with a built-in or an external auxiliary combustion chamber is considered, and the results of tests of the SCSG unit with a turbocompressor and an external auxiliary combustion chamber are presented.
